Bug#992871: darkplaces: Segfault when using custom texturepack

[Bernhard Übelacker]

Dear Maintainer,
I found now another way to get it working by removing the
intermediate function my_setjmp, like in attached patch.

It looks like the compiler needs to be aware of the setjmp.
Before this patch, I tried defining my_setjmp with attribute
returns_twice, but that was not enough.

Kind regards,
Bernhard